A lot of the questions you're asking have been discussed earlier in this thread. Yeah, I know, it's a long thread. I've been participating in it for a little over a year. I did not read from the beginning, but I've hit a few sections in the middle. Here is a thread discussing mods, including some discussion of tubes. Here is a review I wrote comparing the Bravo V2 vs the Schiit Magni, using the Pure i-20 DAC and Schiit Modi DAC. You should visit these boards if you're considering modifying your amp. Note that's a different website. I've got two V2's, one which I just brought back from the dead, after modifying it. Tubes can help open up the high end (telefunken ECC82's in particular), but you really need to replace the MOSFETs if you truly want the high end improved. I'm still tinkering with it, and will write more about it after I'm done. I'm partial to Mullards myself, and I'm really anxious to see what this modified amp sounds like with a vintage Mullard in it.